The dentary of Wareolestes rex (Megazostrodontidae): a new specimen from Scotland and implications for morganucodontan tooth replacement

Abstract

The Middle Jurassic morganucodontan, Wareolestes rex, was previously known from only four isolated molars from Kirtlington, England. There has been debate over the position of the holotype tooth as an upper or lower molar. We describe a new Wareolestes specimen from the Kilmaluag Formation of Scotland: a partial left dentary with two erupted molars, one unerupted molar and three unerupted premolars. Empty alveoli for a canine, p1 and p3 are also present. Through detailed comparison of the morphology of the holotype and our new material, we support the original diagnosis of the holotype Wareolestes as a lower molar, most likely m1. The position of erupted and unerupted replacement teeth in the newly discovered specimen supports a diphyodont pattern of tooth replacement of premolariform dentition in Wareolestes, as suggested for other morganucodontans such as Morganucodon, Megazostrodon and Dinnetherium. However, damage to the dentary means that questions remain regarding the sequence of replacement in Wareolestes along the tooth row.

A Large Morganucodontan Mammaliaform from the Late Jurassic of Germany

“…(Butler et al 2012). The previously youngest unambiguous records of this group were from the Middle Jurassic (Bathonian) of England: Wareolestes rex Freeman, 1979 (also from Scotland), Morganucodon tardus Butler et sigogneau-russell, 2016, Cherwellia leei Butler et sigogneau-russell, 2016 and Stylidens hookeri Butler et sigogneau-russell, 2016 (Freeman 1979, Butler and Sigogneau-Russel 2016, Panciroli et al 2017, as well as Morganucodonta indet., based on a femur from the Middle Jurassic (Bathonian) of Moscow Province, Russia (Gambaryan and Averianov 2001). This new record extends the known stratigraphic range of the Morganucodonta by appoximately 20 Ma.…”

The mandible and dentition ofBorealestes serendipitus(Docodonta) from the Middle Jurassic of Skye, Scotland

“…Highly fossiliferous vertebrate-bearing beds of the Kilmaluag Formation are located on the Strathaird Peninsula and comprise micritic grey limestones with detrital quartz and clay in varying fractions. Vertebrate remains include fish and sharks, turtles, crocodilomorphs, pterosaurs, lepidosaurs, choristoderes, mammaliaforms and tritylodontids, as well as some dinosaur fossils (Waldman and Savage, 1972;Evans et al, 2005;Barrett, 2006;Anquetin et al, 2009Anquetin et al, , 2010Wills et al, 2014;Close et al, 2016;Panciroli et al, 2017aPanciroli et al, , 2017bPanciroli et al, , 2018.…”

“…Docodonta were most diverse in the Middle Jurassic, and had a Laurasian distribution-this is with the possible exception of Gondtherium from Toarcian sediments in India Manhas, 2001, 2007). However, due to a paucity of material and poor preservation, the docodont affinities of mammaliaforms including the cladotherian mammal Palaeoxondon ooliticus, and the morganucodontan Wareolestes rex (Close et al, 2016;Panciroli et al, 2017aPanciroli et al, , 2018b. Material found during field work in 2016 includes another dentary of Borealestes (NMS G.2018.27.1, found by EP).…”

Tissue Mechanical Forces and Evolutionary Developmental Changes Act Through Space and Time to Shape Tooth Morphology and Function

“…Perhaps the shortened period of cranial bone growth thought to be responsible for reducing the number of tooth generations was, more broadly, a shortening of the developmental period of multiple structures in the cranium, including teeth. The continued discovery of early mammal fossil material can provide additional specimens to further investigate the link between skull growth rate and tooth replacement, furnishing important historical context for the morphological setting in which the modification of the dental stem cells occurred.…”